1. Field of the Invention
This invention relates to energy conservation, and particularly to recovering normally unused heat from domestic hot water pipes.
Most existing plumbing systems were designed without considering the present high cost of energy. Hot water is typically piped substantial distances from a heater tank to outlets, and after each use of hot water, heat remaining in the pipe water and walls dissipates and is lost. The pipes must be refilled with hot water for the next use. The water system in a typical home may use approximately one ounce of heating oil, one cubic foot of natural gas, or 250 watt-hours of electricity to heat a gallon of water, and waste as much as twenty-five gallons of hot water per day or nine thousand gallons per year. The increasing cost of energy makes it important to minimize the waste in heating water.
2. Description of the Prior Art
Insulation is the most common way to minimize heat loss in hot water lines, but heat is still lost at a rate depending upon the insulation.
An automatic hot water recovery system is disclosed in U.S. Pat. No. 4,321,943. That system uses a pressure reducer to lower the pressure in a water heater tank and hot water pipe when the hot water outlet is opened to below that of the associated water main and cold water pipe. A bridge conduit from the cold water pipe to the hot water pipe directs a slight flow of cold water from the higher pressure cold water pipe into the lower pressure hot water pipe. When the hot water outlet is closed, an air pocket in the heater tank works as a pneumatic spring to return hot water, and cold water displaces hot water otherwise left standing in the pipe back into the heater tank. The cold water backflow continues, transferring heat from the heated pipe walls into the tank, until the pressure in the tank rises to equal the pressure in the cold water main.
Although the prior art system works well, it depends upon pressure provided by the air pocket inside the heater, which requires some disassembly of the tank and installation of extra pipes.